Move to docker hub from gcr

[jtotoole]

Related PR: https://github.com/mediacloud/systems/pull/229 Original issue: https://github.com/mediacloud/backend/issues/794

@pypt Do you think we need to pass the new Docker Hub credentials as args in the dev scripts, along the lines of what was reversed in this PR (e.g. here)? Even without such arguments added to those dev scripts, the images can be built and pushed correctly at present (new Docker Hub repos here).

[pypt]

No, why pass those credentials? One is supposed to "docker login" using their own Docker Hub user on their own laptop to be able to push something. If someone quits Media Cloud, we would then have to change those shared credentials on all developer computers instead of simply removing a specific user from Docker Hub organisation.

[jtotoole]

Cool that was my assumption, just wanted to make sure. The only test fails here are related to Crimson Hexagon, so I think this is good to go assuming it right solid to you.